Method of making a tack-free gel

ABSTRACT

A process of making a tack-free gel is disclosed comprising the steps of providing a mold defining a mold cavity, the mold cavity comprising a plastic material; pouring or injecting a molten gel having a high molding temperature into the mold cavity; and forming the tack-free gel as a thin layer of plastic of the mold cavity is melted over the gel. The forming step further comprises cooling the gel from the molten state to a solidified state. The melting temperature of the plastic material is lower than the molding temperature of the gel; and the higher the temperature differential, the greater the melting of the plastic material and the thicker the layer of the plastic material on the surface of the gel. The mold may be formed of low-density polyethylene (LDPE).

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation of U.S. application Ser. No.10/913,565, filed on Aug. 5, 2004, now abandoned which claims thebenefit of U.S. Provisional Application No. 60/492,949, filed on Aug. 6,2003, now abandoned and is a continuation-in-part of U.S. applicationSer. No. 10/776,387, filed on Feb. 10, 2004, now U.S. Pat. No.7,727,255, which is a continuation of International Application No.PCT/US02/15696, filed on May 14, 2002, which claims the benefit of U.S.Provisional Application No. 60/312,683, filed on Aug. 14, 2001, nowabandoned all of which are fully incorporated herein by reference.

BACKGROUND OF THE INVENTION

1. Field of the Invention

This invention generally relates to gels having tacky surfaces and, morespecifically, to surface treatments which will render the gel tack-free.

2. Discussion of Related Art

A “gel” is often defined as a semisolid condition of a precipitated orcoagulated colloid. Within this definition, gels can differ widely. Onone end of the spectrum gels are more fluid in nature but have somesolid properties. An example of such a gel might be a gel toothpaste. Atthe opposite end of the spectrum, the gels are considered solids withsome fluid properties.

It is toward this end of the spectrum that gels are commonly used tofacilitate load distribution. Gels enhance this function by offering ahigh degree of compliance which basically increases the amount of areaavailable to support a load. With an increased area of support, the loadis accommodated at a considerably reduced pressure. Particularly wherethe human body is involved, a reduced pressure is desirable in order tomaintain capillary blood flow in body tissue. It is with this in mindthat gels are commonly used for bicycle seats, wrist pads, insolesupports, as well as elbow and shoulder pads.

While the advantageous properties of gels have made them candidates formany applications, one disadvantage has seriously limited their use.Most gels are extremely tacky. This characteristic alone makes themdifficult to manufacture and aggravating to use.

Attempts have been made to produce gels that are naturally non-tacky.But such attempts unfortunately have resulted in an intolerablesacrifice of the advantageous properties. Attempts have been made toenclose the gels in a non-tacky pouch. This has also tended to mask theadvantageous properties and to significantly increase manufacturingcosts. Powders and lubricants have been applied to the tacky surfaceswith results limited in both duration and effect.

Gels have also been of particular interest in the formation of sealswhere the high compliance and extensive elongation of the gel are ofconsiderable value. Such is the case with seals used in trocars andother surgical access devices, where a seal must be formed both in thepresence of a surgical instrument and in the absence of a surgicalinstrument.

In general, a trocar is a surgical device intended to provide tubularaccess for surgical instruments across a body wall, such as theabdominal wall, and into a body cavity, such as the abdominal cavity.Often, the body cavity is pressurized with a gas, typically carbondioxide, to enlarge the operative volume of the working environment.Under these conditions, the trocar must include appropriate seals toinhibit loss of the pressurizing gas through the trocar. Thus, a zeroseal must be provided to seal the working channel of the trocar in theabsence of the instrument, and an instrument seal must be provided toseal the working channel in the presence of the instrument.

Most recently, both zero seals and instrument seals have been providedby a pair of rollers disposed on opposing sides of the working channel.The rollers have been formed of a gel material providing a high degreeof compliance, significant tear strength and exceptional elongation. Asnoted, however, the best gel materials tend to exhibit surfaces that arevery tacky. The use of a tacky gel can make the processes ofmanufacturing and using the gel seals extremely difficult. Thedisadvantages are increasing in this application, where a tacky gel alsoproduces significant drag forces during instrument insertion.Furthermore, the tacky surfaces tend to draw and retain particulatematter during the manufacturing and handling processes. For thesereasons it has been even more desirable to render the highly tacky gelsurfaces non-tacky in the case of medical devices such as trocars.

Many attempts have been made to facilitate handling the rollers duringmanufacture and to lower instrument drag forces during use. For example,use of lubricants such as silicone oil, KY jelly, and Astroglide, havebeen applied to the surface to reduce tackiness. Unfortunately, theselubricants tend to dry out over time leaving the gel in its naturaltacky state. Non-tacky gels have also been investigated. The non-tackygels, however, are not particularly heat tolerant, as low amounts ofheat can rapidly cause the materials to take a set and distortparticularly under compressive loads. This can occur over an extendedperiod of time, for example, even at normal room temperatures.

SUMMARY OF THE INVENTION

In accordance with the present invention, a gel material having all ofthe advantageous properties previously discussed is further blessed witha non-tacky surface that can be provided at the earliest possibleopportunity, during the molding step of the manufacturing process. Fromthe time when the molten gel material first achieves its solidcharacteristics, it is provided with a non-tacky surface. In the case ofa trocar seal, significant drag forces are avoided during the process ofinstrument insertion. Moreover, the advantages of high compliance,significant tear strength, and exceptional elongation are maintainedwithout any of the disadvantages associated with a tacky device.

In a first aspect of the invention, a process of making a tack-free gelis disclosed comprising the steps of providing a mold defining a moldcavity, the mold cavity comprising a plastic material; pouring orinjecting a molten gel having a high molding temperature into the moldcavity; and forming the tack-free gel as a thin layer of plastic of themold cavity is melted over the gel. More specifically, the forming stepfurther comprises cooling the gel from the molten state to a solidifiedstate. The mold providing step may further comprise the step ofinjecting or spraying the mold cavity with the plastic material. It isappreciated that the melting temperature of the plastic material islower than the molding temperature of the gel and, in this aspect, thedifference in the melting temperature of the plastic material and themolding temperature of the gel is in a range of about 20° F. to about100° F. It should be noted that the higher the temperature differential,the greater the melting of the plastic material and the thicker thelayer of the plastic material on the surface of the gel.

The mold may be formed of low-density polyethylene (LDPE) and has amelting temperature of about 240° F. With the process of the invention,the heat of the molten gel at its molding temperature is transferred tothe surface of the LDPE mold so as to melt a thin layer of the LDPE. Thesolidified gel may be a cylindrical shape having a first opposing end, asecond opposing end and a cylindrical body. The mold may comprise a moldbase having a plurality of mold holes forming a plurality of moldcavities, each of the mold holes comprising an axial pin to mold anaxial hole through a center of the gel, an LDPE cylinder providing apredetermined inside diameter for the mold, and an LDPE disc mounted onthe axial pin and disposed at the bottom of each mold cavity in the moldbase. After each molding process, the LPDE cylinder may be replaced. Theprocess of the invention may further comprise the step of dabbing atleast one of the opposing ends in a low-friction powder such aspolytetrafluoroethylene (PTFE) and a lubricant. In another aspect, themold may further comprise a mold top disposed axially of the mold baseand comprises a plurality of holes forming a plurality of cavities, eachof the mold top holes is adapted to receive the LDPE cylinder, and asecond LDPE disc disposed at the top of each mold cavity of the moldtop.

In another aspect of the invention, the plastic material may be formedfrom at least one of PVC, ABS, acrylic, polycarbonate, clearpolycarbonate, Delrin, acetal, polypropylene and high-densitypolyethylene (HDPE). The process of the invention may further comprisethe step of tumbling or coating the gel in a lubricious material,applying a lubricious coating to the gel in a vacuum deposition process,dipping the gel in a lubricious material, or spraying the solidified gelwith a lubricious material to further facilitate the non-tackinesssurface of the gel. The lubricious material includes Parylene.

In yet another aspect of the invention, a process of making a tack-freegel by co-extrusion is disclosed comprising the steps of extruding anelongate sleeve formed of a plastic material around a molten gel havinga high molding temperature, the elongate sleeve having an axis and adiameter; pressurizing the molten gel to control the diameter of thefilled elongate sleeve; and cooling the filled elongate sleeve to formthe tack-free gel. The plastic material of the elongate sleeve may below-density polyethylene (LDPE). The process may further comprise thestep of radially cutting the elongate sleeve into individual segmentshaving predetermined lengths, and removing the gel by squeezing thesleeve and pulling the gel from the sleeve. With this aspect of theinvention, the gel may have a cylindrical shape having a first opposingend, a second opposing end and a cylindrical body. The process mayfurther comprise the step of dabbing at least one of the opposing endsin a low-friction powder, which may include at least one ofpolytetrafluoroethylene (PTFE) and a lubricant, tumbling or coating thegel in a lubricious material, applying a lubricious coating to the gelin a vacuum deposition process, dipping the gel in a lubriciousmaterial, or spraying the gel with a lubricious material. The lubriciousmaterial includes Parylene.

Another aspect of the invention is directed to a trocar being adapted toprovide access for a surgical instrument through a body wall and into abody cavity, the trocar comprising a cannula having a proximal end and adistal end, a seal housing communicating with the cannula to define aworking channel, a seal assembly disposed within the seal housing, atleast one roller included in the seal assembly and having an axlesupported by the seal housing, and the roller having a tack-free surfaceand properties for forming a zero seal in the absence of the instrument,and an instrument seal in the presence of the instrument. With thisaspect, the roller is pivotal with the axle relative to the sealhousing. The tack-free surface may be formed of LDPE, and the roller mayfurther comprise a lubricious coating including at least one ofpolytetrafluoroethylene (PTFE) low-friction powder or a lubricantincluding Parylene.

In a final aspect, a medical access device is disclosed comprising atubular member having an elongate configuration, at least one walldefining with the tubular member a working channel sized and configuredto receive an instrument, and a gel disposed in the working channel andbeing adapted to form a seal with any instrument disposed in the workingchannel, wherein the gel includes a non-tacky film to facilitatemovement of any instrument through the working channel. It isappreciated that the film may be formed by a fluoropolymer includingpolytetrafluoroethylene (PTFE). The non-tacky film may be applied as apowder or as a tape over the gel. It is further appreciated that the geland non-tacky film may have properties including an elongation up toabout 1500 percent, and that the gel may be coated with a lubricantincluding Parylene.

These and other features of the invention will become more apparent witha description of the various embodiments and reference to the associateddrawings.

DESCRIPTION OF THE DRAWINGS

The accompanying drawings, which are included in and constitute a partof this specification, illustrate the embodiments of the invention and,together with the description, explain the features and principles ofthe invention. In the drawings:

FIG. 1 a is a side elevation view partially in cross-section of a trocarwith a roller seal assembly;

FIG. 1 b is a side elevation view of the trocar illustrated in FIG. 1 a;

FIG. 2 a is a perspective view of a plastic mold with multiple moldcavities;

FIG. 2 b is a perspective view of a gel roller with an outer layer ofmold plastic;

FIG. 2 c is a perspective view of a metal mold and multiple cylindersand discs each associated with an individual mold cavity;

FIG. 2 d is a perspective view showing the mold cylinders disposed inthe mold base;

FIG. 3 is a side elevation view illustrating a step of dabbing a tackygel surface into powder;

FIG. 4 is a side elevation view similar to FIG. 1 b and illustrating asingle low friction disc mounted between a tacky roller surface and theseal housing;

FIG. 5 is a schematic view illustrating co-extrusion of an LDPE sleeveand a gel;

FIG. 6 is a perspective view of base and top molds used in an injectionmolding operation;

FIG. 7 illustrates a method for applying a coating by vacuum deposition;

FIG. 8 is a perspective view illustrating application of a coating in adipping process;

FIG. 9 is a perspective view illustrating application of a coating byspraying;

FIG. 10 is a perspective view illustrating an application of a coatingby tumbling;

FIG. 11 is a perspective view of a hand port wherein a gel seal isoverlayed with a fluoropolymer film; and

FIG. 12 is a cross-section view taken along lines 12-12 of FIG. 11.

DESCRIPTION OF THE INVENTION

A trocar is illustrated in FIG. 1 and designated by the referencenumeral 10. The trocar 10 is an access device commonly used in surgeriesto provide a working channel 12 across a body wall and into a bodycavity. The working channel 12 in this case is defined by a cannula 14and a seal housing 16. Within the seal housing, a seal apparatus 18 isformed by a pair of opposing rollers 21 and 23. These rollers 21 and 23are typically formed of a gel material 30 that provides the sealapparatus 18 with a high degree of compliance, significant tear strengthand exceptional elongation. In this case, the gel rollers 21 and 23 aremerely representative of any gel structure adapted for use in a medicaldevice, such as the trocar 10.

The gel materials contemplated for the rollers 21 and 23 typically havea high melting temperature and exhibit a tacky surface as previouslydiscussed. These two properties, normally considered disadvantages,become advantages in a method of manufacture of the invention. In thiscase, the gel at a high molding temperature and liquid state, is broughtinto contact with a plastic molding material having a meltingtemperature less than the molding temperature of the gel 30.

A roller mold 25 is illustrated in FIG. 2 a with a plurality of moldcavities or holes 27. In this case, the mold 25 is formed entirely of aplastic material 26 which defines each of the cylindrical mold cavities27. The gel 30 in its high temperature liquid state is poured into eachof the mold holes 27 to form one of the rollers 21, 23. At the highmolding temperature, the gel 30 initially melts a thin layer 32 of themold plastic 26 which cools onto the gel surface as illustrated in FIG.2 b. In this process, it is believed that the tacky properties of thegel 30 attract and hold this thin layer 32 of plastic thereby resultingin a non-tacky surface on the gel 30.

With the process of the invention, it is desirable that the meltingtemperature of the plastic material 26 be only slightly lower than themolding temperature of the gel 30. In one aspect, the differential intemperature is in a range of about 20° F. to about 100° F. It isanticipated that the higher this temperature differential, the greaterthe melting of the plastic material, thereby resulting in a thickerlayer of the plastic material on the surface of the gel.

In one example, a gel can be chosen with a gel molding temperature ofabout 450° F. A mold 25 formed of a non-metal, plastic material such aslow-density polyethylene (LDPE) having a melting temperature of about240° F. is particularly suited for this process. With the mold at roomtemperature, and the liquid gel heated to its molding temperature, thegel can be poured into the mold cavities. During and after this moldingstep, the heat of the liquid gel at its molding temperature istransferred to the surface of the plastic mold and in fact melts a thinlayer of the LDPE. At this point, the mold 25 and gel 30 rapidly cooland the melted LDPE forms the thin layer 32 on the outer surface of thesolidified gel 30. As the gel solidifies, its naturally tacky surfaceattracts and holds the thin LDPE layer 32 to the outer surface. Thisthin layer 32 of LDPE provides the resulting gel roller 21 with anon-tacky surface.

Using the mold formed entirely of the LDPE plastic will graduallyincrease the size of the mold cavities 27 as succeeding interior layers32 of the LDPE are removed from the mold cavities 27. One way ofaddressing this problem is to provide a mold base 41 having a pluralityof mold holes 43 as illustrated in FIG. 2 c. In this case, the moldholes 43 are formed with an axial pin 45 which can be used to mold anaxial hole through the center of the roller 21. Each of the mold holes43 in the base 41 can then be lined with an LDPE cylinder 47 providing apredetermined inside diameter for the mold. In addition, an LDPE disc 50can be mounted on the pin 45 and disposed in the bottom of each moldcavity 43 in the base 41. In this case, the cylinder 47 and disc 50provide the preferred mold cavities 27 found of LDPE and ready toreceive the gel 30.

With this mold base 41 appropriately filled with the LDPE cylinders 47and discs 50, the molten gel 30 can be poured into the top of eachcylinder 47 to mold each roller 21 with a cylindrical outer surface 52and an axial pin 45. In the manner previously discussed, the hightemperature of the molten gel will melt a layer off the inside of theLDPE cylinder 47 and disc 50 to provide a non-tacky surface on eachroller 21. One advantage provided by the method illustrated in FIG. 3 isthat the LDPE cylinders 47 can be discarded after each molding processand replaced with new LDPE cylinders 47 having the predetermineddiameter.

It will be noted that in the absence of an LDPE disc on the top of themold cavity, one end 56 of the roller 21 will maintain its tackyproperties. Although the single tacky end 56 may not be particularlydetrimental in use, there are several methods that can be implemented tomake the tacky end 56 less tacky. For example, this end 56 can be dabbedin a low friction powder 57, such as PTFE, as shown in FIG. 3. Also, thetacky end 56 can be lubricated to make it less tacky. As a thirdalternative, the tacky end 56 of the roller 21 can be mounted in thetrocar 10 adjacent to a low friction disc 58 as illustrated in FIG. 4.

An alternative method for constructing the rollers 21, 23 with anon-tacky surface might involve the use of co-extrusion techniques. Insuch a process, illustrated in FIG. 5, an elongate sleeve 61 of LDPE canbe extruded around the molten gel 30. In this case, the gel 30 can bepressurized to control the diameter of the filled sleeve 61. After thefilled sleeve 61 is permitted to cool, it can be radially cut intoindividual segments 62 having a predetermined length as illustrated inFIG. 5. The gel 30 can be removed by merely squeezing the sleeve 61 andpulling the gel 30 from the sleeve. Once removed, the gel roller 21 willhave an outer cylindrical surface 63 with an LDPE coating 65, and a pairof opposing ends 67 and 70. In this process, both of the ends 67 and 70of the roller 21 will be uncoated and will therefore have tackysurfaces. These two ends 67, 70 can be addressed in the mannerpreviously discussed with reference to the roller end 56 in FIG. 3.

Another process which might be used to eliminate the tacky ends of theroller 21, might be an injection molding process such as thatillustrated in FIG. 6. In this case both a mold base 72 and a mold top74 are provided to receive an LDPE cylinder 74 and a pair of LDPE discs76 and 78, one on each end of the cylinder 74. Rather than pouring themolten gel 30 into the open top of the cylinder as illustrated in FIG.2, the molten gel 30 in this process would be injected into the LDPEmold cavity 43. The resulting gel roller 21 would have all of itssurfaces, including both ends, coated with a thin layer of LPDE.

The foregoing processes have been discussed with respect to a singleplastic, namely low density polyethylene. It is apparent that othertypes of plastics might be similarly used to provide the desirednon-tacky surface for the gel compounds. Other plastics which might beof advantage in this process could include for example, PVC, ABS,acrylic, polycarbonate, clear polycarbonate, “Delrin” (a trademark ofDupont), acetyl, polypropylene, and high density polyethylene (HDPE). Ofthis group of plastics, the HDPE appears to reduce the tackiness of thegel surface to the greatest extent.

Other types of coatings can be applied to either a tacky or non-tackysurface of the roller 21. One highly lubricious coating is thatmanufactured and sold by Para Tech Coating, Inc. under the trademark“Parylene”. It has been found that this material can be applied to thesurface of the roller 21 by processes including vacuum deposition in achamber 81 (FIG. 7), dipping on a tray 83 (FIG. 8) and spraying on ashelf 85 (FIG. 9). A highly lubricious coating, such as Parylene mayalso be applied in a tumbler 87 as illustrated in FIG. 10. In this case,the rollers 21, 23 being tumbled must already have a non-tacky surfacein order to remain separate during the tumbling process.

Another apparatus and method for addressing the natural tacky propertiesof a gel seal is discussed with reference to FIG. 11. In this view, amedical device in the form of a hand port is adapted to overlay a bodywall, such as an abdominal wall 92, and to provide sealed access to abody cavity, such as an abdominal cavity 93, for a surgical instrument,such as a surgeon's hand 94.

In this embodiment, the hand port 90 includes a rigid or semi-rigid basestructure 96 in the form of a ring 98. A gel material 101, of the typespreviously discussed, can be molded into the ring 98 with portions 103of the gel 101 defining a slit 105. This slit 105, which is ofparticular interest in one aspect of the invention, forms part of aworking channel 107 that extends through the abdominal wall 92 and intothe abdominal cavity 93.

In this embodiment, the ring 98 is similar to the cannula 14 and sealhousing 16 discussed with reference to FIG. 1 a, in that it is disposedaround the working channel 107 and is adapted to form a seal 110 withthe abdominal wall 92.

A second seal 112 is formed between the gel material 101 and the ring 98so there is no communication between the abdominal cavity 93 and regionsexterior of the abdominal wall 92 as long as the slit 105 remainsclosed. In this manner, the hand port 90 functions as a zero seal in theabsence of the surgeon's hand 94, or any other medical instrument.

The highly advantageous properties of the gel material 101 areparticularly beneficial in the hand port 90, where they provide a highdegree of compliance together with elongation or stretch as great as1500 percent. Thus, the gel material 101 is ideally suited to form azero seal in the absence of the surgeon's hand 94, or an instrument sealin the presence of the surgeon's hand 94. It can be seen that the gelmaterial 101 is similar to that previously discussed with respect to therollers 21 and 23 in FIG. 1 a. In that regard, the gel material 101 isdisposed in the base structure and forms the second seal 112 with thebase structure. The gel material 101 will typically have the tackyproperties in its natural state, as previously discussed.

In order to address these tacky properties in the hand port 90, and alsowith respect to the trocar 10 of FIG. 1 a, a film 14 can be applied tothe surface of the gel material 101. This is particularly advantageouswith respect to the portions 103 where the film 114 lines the workingchannel 107 through the hand port 90. When the film 114 is applied toany surface of the gel material 101, it functions to mask the tackyproperties of the gel material 101 greatly facilitating handling of thehand port 90 during manufacture. But in the particular location wherethe film 114 is applied to the portions 103 defining the slit 105, thegel not only masks the tacky properties, but also facilitates movementof the medical instrument such as the surgeon's hand 94 into and throughthe working channel 107. In certain preferred embodiments, the film 114is formed by a fluoropolymer, such as polytetrafluoroethylene (PTFE). Inone method of manufacture, the film 114 is applied as a PTFE powder. Inother processes, the film 114 can be applied as a PTFE tape.

One advantage associated with the PTFE film 114 is the adhesiveproperties which this material exhibits with respect to the gel material101. Although not fully understood, it is believed that the mineral oilpresent in a typical gel 101 is highly attracted to the PTFE where itfacilitates adhesion between the gel material 101 and the film 114.

Another advantage associated with the PTFE film 114 is associated withits stretchability or elasticity. While the film 114 is desirable tomask the tacky properties of the gel 105, it is important that theelongation properties of the gel be maintained. It has been found thatthe elongation of the gel material 101, up to 1500 percent, is generallymatched by the elongation or stretchability of the PTFE film 114. Thus,the gel 101 and PTFE film 114 can be stretched about 1000 percent, andperhaps as much as 1500 percent, from an original state to a stretchedstate without breaking the film 114, and returned from the stretchedstate to the original state.

Although the PTFE film 114 masks the tacky properties of the gel, it isnot necessarily lubricious. If this lubricious property is desired inaddition to the non-tacky properties, the film 114 can be coated with alubricant 116, such as the Parylene and other lubricants previouslydiscussed.

It will be understood that many other modifications can be made to thevarious disclosed embodiments without departing from the spirit andscope of the invention. For these reasons, the above description shouldnot be construed as limiting the invention, but should be interpreted asmerely exemplary of embodiments.

The invention claimed is:
 1. A method of making a tack-free gel,comprising the steps of: providing a mold defining a mold cavity, themold cavity comprising a plastic material; pouring or injecting a moltengel being at a molding temperature into the mold cavity; and melting alayer of the plastic material of the mold cavity onto the molten gel bypermitting the molten gel to contact the mold cavity; wherein the moldcomprises a mold base comprising: a plurality of mold holes forming aplurality of mold cavities, each of the mold holes comprising: an axialpin to mold an axial hole through the gel; a low-density polyethylene(LDPE) cylinder in each mold cavity providing a predetermined insidediameter for the mold; and an LDPE disc mounted on the axial pin anddisposed at the bottom of each mold cavity in the mold base.
 2. Themethod of claim 1 wherein the plastic material has a melting temperaturethat is lower than the molding temperature of the molten gel and themelting temperature of the plastic material differs from the moldingtemperature of the molten gel by about 20° F. to about 100° F.
 3. Themethod of claim 1 further comprising increasing thickness of the meltedlayer of plastic material by selecting a plastic material that has amelting temperature lower than the molding temperature of the molten geland increasing the temperature differential between the meltingtemperature of the plastic material and the molding temperature of themolten gel.
 4. The method of claim 1 further comprising heating gel toliquefy the gel to form a molten gel.
 5. The method of claim 4 whereinthe molding temperature is about 450° F.
 6. The method of claim 1further comprising replacing each LPDE cylinder after each moldingprocess.
 7. The method of claim 1 wherein the mold further comprises amold top disposed axially of the mold base and comprising: a pluralityof mold holes forming a plurality of cavities, each of the mold topholes is adapted to receive each LDPE cylinder; and a second LDPE discdisposed at the top of each mold cavity of the mold top.
 8. The methodof claim 1 further comprises cooling the molten gel to form a solidifiedgel.
 9. The method of claim 8 further comprising dabbing the solidifiedgel in a low-friction powder.
 10. The method of claim 8 forming anopening in the solidified gel.
 11. The method of claim 10 applying alow-friction material to the opening in the solidified gel and whereinthe solidified gel and the low-friction material have an elongation upto about 1500 percent.
 12. The method of claim 8 applying a low-frictionmaterial to the solidified gel.
 13. The method of claim 12 wherein thelow-friction material is formed by a fluoropolymer includingpolytetrafluoroethylene (PTFE) and the plastic material is formed fromat least one of PVC, ABS, acrylic, polycarbonate, clear polycarbonate,Delrin, acetal, polypropylene and high-density polyethylene (HDPE). 14.The method of claim 12 wherein the low-friction material is in the formof tape and further comprising applying a lubricious material to thesolidified gel after applying the low-friction material.
 15. The methodof claim 8 further comprising tumbling the solidified gel in alubricious material.
 16. The method of claim 8 further comprisingapplying a lubricious material to the solidified gel by vacuumdeposition.